make up (one's) mind
1. To make a final decision after a period of consideration. Also seen as "make (one's) mind up." I've made up my mind, and I think we should move after all. I'm not sure what flavor I want—I'm still making my mind up.
2. To become convinced of a particular course of action. Also seen as "make (one's) mind up." Right then and there, I made up my mind that I would become a police officer when I grew up.
Make your mind up.
Fig. Please make a decision.; Please choose. Henry: I don't have all day. Make up your mind. Rachel: Don't rush me. Bob: Make your mind up. We have to catch the plane. Mary: I'm not sure I want to go.